This disclosure generally relates to devices and processes for measuring the intensity of light, and more particularly, to a probe for collecting light in a zone characterized by radiation less than about 270 nanometers and limited access for placing or installing instrumentation.
During fabrication of an integrated circuit, it is well known that undesirable charge buildup can occur such as on the floating gate of an EPROM device, if applicable, and/or other areas of the integrated circuit. This charge buildup can lead to high voltages and cause electrical damage to the circuitry or alter the operation of the device if the charge buildup is not removed or neutralized. Charge buildup can readily occur during one or more of the numerous processing steps common to fabricating the integrated circuit. For example, charge buildup can occur during an annealing process, during metal ashing or etching processes, after via and pad formation steps, and the like. Integrated circuits typically employ 3 to 5 conductive metal layers, which during fabrication includes about 5 to about 7 processing steps that can contribute to charge buildup. It is important to erase the charge buildup as the device is being fabricated.
Charge buildup can be removed by periodically exposing the integrated circuit during fabrication to narrow-band ultraviolet radiation sources. Current charge-removal processes typically utilize a mercury electrode lamp that produces a narrow-band spectrum at a wavelength of about 254 nanometers (nm). The mercury lamp emits high-energy photons that propagate through the integrated circuit stack to impart energy to the stored electrons and trapped electrons as well as other charges that may be present. These energized electrons overcome the energy barriers that previously confined the electrons and other charges such that recombination can occur between the electrons and the electron holes or positive charges within the integrated circuit or be drained off of the device, thereby erasing or dissipating the charge buildup that occurred during the fabrication process. The narrow-band UV light exposure also increases the mobility of charges on other areas of the integrated circuit. However, the use of narrow band radiation sources is relatively slow and moreover, may not penetrate to those areas that require removal of the charge buildup since the integrated circuit is generally formed of many different types of layers, some of which fully adsorb or prevent the narrow band radiation from exposing subjacent layers.
Another process and apparatus includes exposing the integrated circuit to broadband radiation sources at low wavelengths ranging from ultraviolet wavelengths to vacuum ultraviolet wavelengths. Orders of magnitude in efficiency are obtained with devices and process employing broadband radiation relative to the narrow band wavelength exposure tools described above, providing faster throughput and more efficient removal of charge buildup. Moreover, since a broadband radiation pattern is employed, absorption by the various layers of the integrated circuit is overcome. The wavelengths of interest for the broadband radiation exposure are generally defined at about 270 nm to about 180 nm.
It is desirable to accurately monitor the wavelengths employed for charge erasure. For example, absorption of light in air and in the materials used in the fabrication of the integrated circuit can attenuate the light. Current radiometers are impractical or ineffective for use at wavelengths less than about 270 nm. Many of the commercially available radiometer devices include materials that absorb at the wavelengths of interest. Moreover, current radiometers and probes typically measure a wide range of wavelengths that overlap with the wavelengths of interests, thereby diminishing the sensitivity of the radiometer or probe for the range of interest. Still further, it is desirable to have the capability of measuring the emitted spectrum from the bulb under actual processing conditions (as opposed to measuring the spectrum of the bulb itself) since there could be many variables that affect transmission of the light from the bulb to the wafer location within the process chamber.